Evidence from controlled trials suggests that ingestion of 0.4 mg of folic acid per day in the periconceptional period is effective in preventing neural tube defects (NTD). For this reason, most countries recommend that women planning pregnancy take folic acid supplements in the periconceptional period, and some countries even fortify stable foods with folic acid. Denmark exemplifies a country with a relatively conservative attitude with respect to taking action in these matters. In 1999, a national information campaign was launched that recommended women planning pregnancy take 0.4 mg of folic acid periconceptionally, but with the moderation that women who eat a healthy diet do not need to take folic acid supplement. The campaign was repeated during 2001. The results of the latter campaign were evaluated by using data from a national survey among pregnant women conducted simultaneously with the campaign by the Danish National Birth Cohort. An increase in the proportion of folic acid users took place concomitantly with the launching of the information events, but the increase was limited. Among women who did not plan their pregnancy, a small proportion had taken folic acid supplements periconceptionally, and this proportion did not change concomitantly with the campaign. Young age and low education were factors associated with low likelihood of taking folic acid. It seems that different and more efficient actions are needed if a more substantial proportion of Danish women and their fetuses are going to benefit from the knowledge that folic acid supplementation in the periconceptional period can prevent NTD.